Method of forming mask pattern

ABSTRACT

The present invention relates to a method of forming a mask pattern. According to the present invention, a negative photoresist layer is formed over a substrate. Some regions of the negative photoresist layer are exposed. The exposed negative photoresist layers are developed. A positive photoresist layer is formed over the substrate including negative tone working photoresist layers. The substrate is baked so that a hydrogen gas is diffused into the positive photoresist layers at boundary portions of the negative tone working photoresist layers. The positive photoresist layers into which the hydrogen gas is diffused are developed.

BACKGROUND OF THE INVENTION

The present invention relates to a method of forming a mask pattern and, more particularly, to a method of forming a mask pattern, in which it can reduce a pattern pitch through exposure and development according to a combination of a chemically amplified negative photoresist and a chemically amplified positive photoresist.

As semiconductor products are miniaturized and high integrated, there is a growing interest in the pattering technologies for forming a pattern in order to improve a new function of devices. Current patterning technologies with a high integration level have been developed as nuclear technologies of semiconductor fabrication, and a photolithography process is generally used. In this photolithography process, a photoresist (PR) (that is, a chemical material that reacts according to whether light is irradiated) is coated to form a photoresist layer. The photoresist layer is exposed and developed, thus forming a mask pattern. The underlying layer is selectively etched and patterned using the formed mask pattern.

In general, the process capability limit (resolutions) of a photoresist layer exposure equipment used at the time of patterning is represented by the half pitch, which is half the pattern pitch defined as the sum of the line pattern and the space.

The resolution of exposure equipment that has been developed so far is 45 nm on the basis of the half pitch. It is necessary to reduce the pattern pitch or the half pitch in order to increase a net die.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to form a mask pattern having a pattern pitch, which is half the resolution of an exposure equipment through exposure and development according to a combination of a chemically amplified negative photoresist and a chemically amplified positive photoresist.

In accordance with a method of forming a mask pattern according to the present invention, a negative photoresist layer is formed over a substrate. Some regions of the negative photoresist layer are exposed. The exposed negative photoresist layers are developed. A positive photoresist layer is formed over the substrate including negative tone working photoresist layers. The substrate is baked so that a hydrogen gas is diffused into the positive photoresist layers at boundary portions of the negative tone working photoresist layers. The positive photoresist layers into which the hydrogen gas is diffused are developed.

A Bottom Anti-Reflective Coating (BARC) layer may be further formed before the formation of the negative photoresist layer. Each of the negative photoresist layer and the positive photoresist layer may be formed using a chemically amplified photoresist.

The sum of a space between the negative tone working photoresist layers may have a pitch, which is twice a resolution of an exposure equipment. The positive photoresist layer may be formed so that a thickness on a top of the negative tone working photoresist layer is thinner than a thickness of the hydrogen gas, which will be diffused into a side portion of the negative tone working photoresist layer, in consideration of the thickness of the hydrogen gas to be diffused into the side portion of the negative tone working photoresist layer through baking. The positive photoresist layer may be formed so that a thickness of the hydrogen gas diffused into a lateral portion of the negative tone working photoresist layer is thinner than a thickness on a top of the negative tone working photoresist layer.

The mask pattern may have a pattern pitch, which is controlled to have a target distance by removing the positive photoresist layer including the hydrogen gas diffused into a side portion of the negative tone working photoresist layer. The mask pattern may include the negative tone working photoresist layer and a positive tone working photoresist layer, which are spaced apart from each other at a space and are alternately formed.

The mask pattern is formed so that a sum of the negative tone working photoresist layer or the positive tone working photoresist layer and the space has the same pattern pitch as a resolution of an exposure equipment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1F are sectional views illustrating a method of forming a mask pattern according to an embodiment of the present invention.

DESCRIPTION OF SPECIFIC EMBODIMENTS

Now, a specific embodiment according to the present invention will be described with reference to the accompanying drawings.

However, the present invention is not limited to the disclosed embodiment, but may be implemented in various manners. The embodiment is provided to complete the disclosure of the present invention and to allow those having ordinary skill in the art to understand the scope of the present invention. The present invention is defined by the category of the claims.

FIGS. 1A to 1F are sectional views illustrating a method of forming a mask pattern according to an embodiment of the present invention.

Referring to FIG. 1A, a Bottom Anti-Reflective Coating (BARC) layer 110 is formed on a substrate 100. The BARC layer 110 functions to control reflection light of an exposure light source, which is reflected from the surface of the substrate 100. The BARC layer 110 may not be formed, if appropriate.

A negative photoresist layer 120 is formed on the BARC layer 110. The negative photoresist layer 120 may be formed using a chemically amplified resist.

The chemically amplified resist refers to a resist having the quantum yield of 100% or more. A reaction inhibitor, including resin and a Photo Acid Generator (PAG) as integral components, may be used as the chemically amplified resist in order to improve the contrast and control solubility. The chemically amplified resist may employ a matrix resin in which part of polyhydroxystyrene (PHST) resin is substituted with a t-buthoxycarbonyl (t-BOC) radical at an appropriate ratio (n/m) in order to control solubility with respect to a developer. In this case, the negative photoresist layer 120 may be formed using a spin coating method.

Referring to FIG. 1B, some regions of the negative photoresist layer 120 are exposed. ArF or KrF can be used as the exposure light source. As described above, acid formed by this exposure makes O-t-BOC a state where it is dissolved in an alkaline solution by resolving O-t-BOC into O-H. A hydrogen (H+) gas obtained as a by-product is used to deprotect surrounding t-BOC and performs an amplification action. Thus, exposed negative photoresist layers 120 a including the hydrogen (H+) gas is formed.

In particular, according to the present invention, a pattern pitch is controlled by removing a thickness as thick as the hydrogen (H+) gas, which is diffused into a positive photoresist layer (not shown) of the sidewalls of the exposed negative photoresist layers 120 a through a subsequent baking process. The pattern pitch is controlled by controlling the thickness of the hydrogen (H+) gas diffused into the positive photoresist layer through control of the amount of exposure.

Referring to FIG. 5C, the exposed negative photoresist layers 120 a are developed. The hydrogen (H+) gas formed by exposure generates initiates a crosslinking reaction with the photoresist, so the exposed photoresist layers 120 a remain without being dissolved in a developer. Thus, negative tone working photoresist layers 120 b (that is, a photoresist in which exposed portions remain as patterns after exposure) are formed.

The sum of a first space 120 c between the negative tone working photoresist layers 120 b is defined by a pattern pitch P1, and is twice an exposure equipment resolution.

Referring to FIG. 1D, a positive photoresist layer 130 is formed over the substrate 100 including the negative tone working photoresist layers 120 b. The positive photoresist layer 130 may be formed from a chemically amplified resist using a spin coating method.

The thickness of the positive photoresist layer 130 formed on the negative tone working photoresist layers 120 b may be thinner than a thickness, which is removed due to the diffusion of the hydrogen (H+) gas into the lateral sides of the negative tone working photoresist layers 120 b through a subsequent baking process, so that a developer can infiltrate below the positive photoresist layer (not shown) into which the hydrogen (H+) gas has been diffused.

Referring to FIG. 1E, the substrate 100 over which the positive photoresist layer 130 is formed is baked. Thus, the hydrogen (H+) gas is diffused to a specific thickness on the entire surface of the negative tone working photoresist layers 120 b, thus forming positive photoresist layers 130 a into which the hydrogen (H+) gas has been diffused. At this time, the positive photoresist layer 130 a into which the hydrogen (H+) gas is diffused is formed such that a thickness on the lateral side of the negative tone working photoresist layer 120 b is thicker than that at the top of the negative tone working photoresist layer 120 b.

Referring to FIG. 1F, only the positive photoresist layers 130 into which the hydrogen (H+) gas is diffused are selectively developed. In this case, the positive photoresist layers 130 into which the hydrogen (H+) gas is diffused are dissolved in a developer and thus removed through a decomposition reaction of the hydrogen (H+) gas and the photoresist. Consequently, positive tone working photoresist layers 130 b are formed.

Accordingly, a mask pattern 140 in which the negative tone working photoresist layer 120 b, and the positive tone working photoresist layer 130 b thicker than the negative tone working photoresist layer 120 b are repeated alternately with them being spaced apart from each other at a second space 130 c is completed. At this time, the positive tone working photoresist layers 130 b are formed between the negative tone working photoresist layers 120 b. Thus, the distance of the second space 130 c is narrower than the first space 120 c of FIG. 1C as much as a distance in which the positive tone working photoresist layer 130 b and the second space 130 c are added.

As described above, the mask pattern 140 has a pattern pitch P2, which is defined as the sum of the negative tone working photoresist layer 120 b or the positive tone working photoresist layer 130 b, and the second space 130 c between the negative tone working photoresist layer 120 b and the positive tone working photoresist layer 130 b. The pattern pitch P2 becomes a target distance. Therefore, the pattern pitch P2 of the mask pattern 140 according to the present invention is ½ smaller than the pattern pitch P1, which is formed through exposure and development employing only the negative photoresist layer 120. In other words, the mask pattern 140 according to the present invention can implement a pattern pitch having the same distance as that of the resolution of an exposure equipment.

The mask pattern 140 formed as described above is used as a hard mask for forming an actual pattern, such as a gate electrode or a bit line in the semiconductor device process. Accordingly, a pattern pitch can be reduced and therefore a net die can be increased.

According to the present invention, a mask pattern having a pattern pitch, which is ½ smaller than that formed using only one kind of a photoresist layer in the prior art, can be formed through exposure and development according to a combination of a chemically amplified negative photoresist and a chemically amplified positive photoresist.

Further, according to the present invention, a net die can be increased by applying the mask pattern having a reduced pattern pitch to the fabrication process of semiconductor devices.

The present invention is not limited to the disclosed embodiment, but may be implemented in various manners. The embodiment is provided to complete the disclosure of the present invention and to allow those having ordinary skill in the art to understand the scope of the present invention. The present invention is defined by the category of the claims. 

1. A method of forming a mask pattern, comprising: forming a negative photoresist layer over a substrate; exposing some regions of the negative photoresist layer; developing the exposed negative photoresist layers; forming a positive photoresist layer over the substrate including negative tone working photoresist layers; baking the substrate so that a hydrogen gas is diffused into the positive photoresist layers at boundary portions of the negative tone working photoresist layers; and developing the positive photoresist layers into which the hydrogen gas is diffused.
 2. The method of claim 1, further comprising forming a Bottom Anti-Reflective Coating (BARC) layer before the formation of the negative photoresist layer.
 3. The method of claim 1, wherein each of the negative photoresist layer and the positive photoresist layer is formed using a chemically amplified photoresist.
 4. The method of claim 1, wherein a sum of a space between the negative tone working photoresist layers has a pitch, which is twice a resolution of an exposure equipment.
 5. The method of claim 1, wherein the positive photoresist layer is formed so that a thickness on a top of the negative tone working photoresist layer is thinner than a thickness of the hydrogen gas, which will be diffused into a side portion of the negative tone working photoresist layer, in consideration of the thickness of the hydrogen gas to be diffused into the side portion of the negative tone working photoresist layer through baking.
 6. The method of claim 1, wherein the positive photoresist layer is formed so that a thickness of the hydrogen gas diffused into a lateral portion of the negative tone working photoresist layer is thinner than a thickness on a top of the negative tone working photoresist layer.
 7. The method of claim 1, wherein the mask pattern has a pattern pitch, which is controlled to have a target distance by removing the positive photoresist layer including the hydrogen gas diffused into a side portion of the negative tone working photoresist layer.
 8. The method of claim 1, wherein the mask pattern includes the negative tone working photoresist layer and a positive tone working photoresist layer, which are spaced apart from each other at a space and are alternately formed.
 9. The method of claim 8, wherein the mask pattern is formed such that a sum of the negative tone working photoresist layer or the positive tone working photoresist layer and the space has the same pattern pitch as a resolution of an exposure equipment. 